Add int16 support to PACK/UNPACK #4459

Job	Run time
no-labels	1s
ci-ready-to-merge	3s
ci-run	1s
ci-run-full	2s
call-ci / Bazel asan (presubmit)	14m 24s
call-ci / Bazel msan (presubmit)	14m 7s
call-ci / Bazel (presubmit)	17m 22s
call-check-tflite-files / Check PR Modifies TfLite Files	37s
call-ci / Bazel TFLite Tools (presubmit)	1m 46s
call-ci / Cortex-M Bluepill No Release (presubmit)	8m 33s
call-ci / Code Style (presubmit)	1m 25s
call-ci / Cortex-M Bluepill Release (presubmit)	7m 31s
call-ci / Cortex-M Bluepill Renode (presubmit)	4m 29s
call-ci / Cortex-M QEMU Unit Tests (presubmit)	7m 16s
call-ci / Project Generation (presubmit)	9m 55s
call-ci / Makefile x86 Default (presubmit)	6m 59s
call-ci / Makefile x86 No TFLite Static Memory (presubmit)	5m 48s
call-ci / Makefile x86 Out Of Tree (presubmit)	3m 33s
call-ci / Makefile x86 Release (presubmit)	11m 51s
call-hexagon / Hexagon Build Test (presubmit)	8m 54s
call-xtensa-presubmit / Hifi3z Unit Tests (presubmit)	23m 18s
call-xtensa-presubmit / Hifi5 Unit Tests (presubmit)	19m 46s
call-xtensa-presubmit / Vision P6 Build (presubmit)	12m 15s
PR has Bug	1s
	2h 59m 57s

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